This invention relates generally to tension regulators and, more particularly, to a cable tension regulator capable of receiving an input force and transmitting an output force for use in mechanical control.
Cables are often used to control flight control surfaces such as elevators, rudders or ailerons, or valves or other mechanisms in an airplane. Control equipment in other vehicles or various other types of machinery may also employ closed loop cable control systems. Tension in cables is subject to variation due to changes in temperature, structural deflection and other environmental influences. For instance, rapid descent or acceleration of an aircraft may cause the cables to become taught or loose due to rapid airframe structural changes caused by gravitational loading on the aircraft. Since cables are often used to control flight critical surfaces, it is important that the cables are maintained constantly in tension so as not to cause loss of control.
One solution is to rig the cables in the control system so that they are under high tension. Therefore, even if there is some reduction in tension the cables will not go slack and the control surface can be controlled normally. However, high tension in the cables causes a corresponding increase in friction forces in the control system which resists movement of the cables. Thus, it is desirable to maintain as low a tension on the cables as possible without causing loss of control. Cable tension regulators are employed to permit the tension in the cables to be relatively low, but are responsive to changes in cable tension so as to constantly maintain at least a minimum tension in the cables.
Presently available tension regulators have one or more compression springs constructed to exert a tensioning force on the cables. A locking mechanism on the tension regulator locks out operation of the spring when control forces are applied to the cables. Otherwise, the spring would tend to be compressed by these forces producing lost motion in the control. The locking mechanism may operate when there is unequal tension in the cables, such as occurs when a control force is applied. However, in the absence of a control force, the spring permits contraction of the cables and also maintains a tension on the cables if they become further elongated.
In the control circuit, the control cables are connected to a pulley to either provide input to turn the pulley which in turn provides motion to an output member and effect movement of a control surface, or receive input from an input member which causes rotation of the pulley to effect movement of the cable to move a control surface. The tension regulator is frequently separate from the pulley or load transferring device and adds additional complexity and weight to the system. Tension regulators incorporated into the pulleys tend to be complex, requiring numerous parts and increasing the risk of failure. These regulators generally consist of two opposing quadrants acting as a pulley. The pulley must be large enough to take up both cable elongation and contraction and provide input and output to the system.